I think I know what happened in your case, @Dohregard
This was the key, since the monument wasn’t inside any of the storages.
This is a bug where, if the crafter gets interrupted right after they finished crafting, they will leave the crafted item on the workbench (it will disappear when you craft another of the same item, but you will lose the one that got stuck on the workbench).
In this case, since the kiln is so huge, we couldn’t see the item, but if you try to make the camera go through the kiln, you will see that the monument is still there.
Unfortunately, I don’t know of a way to retrieve it from there, so you might need to craft another one
I reported this to the devs some time ago, and Linda has fixed it so that the crafters should never leave items on top of their workbenches again. This fix will be in when we release Alpha 20.
Not sure about @paragouldgamer 's case. When dump_inaccessible_items returns 0, it shoud mean that the item is iconic at some place, and maybe the hearthlings can’t reach it for whatever reason.
I removed all your buildings, and went to the placement UI and placed all the rugs from there and now there are 6 rugs on the floor. However I have no clue of where the missing rug is. My guess is that it might have fallen on top of a wall or on a roof or some other place that makes it hard to see where it is.